The hypothesis of this program is that Fabl, the conserved enoyl reductase enzyme in the bacterial fatty acid biosynthesis pathway, is a target for the development of preclinical lead compounds with broad spectrum activity against priority pathogens, including F. tularensis, B. pseudomallei, and Y. pestis. Based on this approach, we have developed inhibitors with potent activity against the Fabl enzyme from F. tularensis and 8. pseudomallei. Significantly, we have demonstrated efficacy in an animal model of tularemia. Encouraged by this progress and due to the need to develop chemotherapeutics against other priority pathogens, we will extend our studies to include the development of potent in vivo antibacterial agents against 6. pseudomallei and Y. pestis. Our overall goal is to rapidly progress lead compounds into animal models of infection for efficacy testing with the following Specific Aims: Aim 1: Rational Optimization of Lead Compounds Against F. tularensis. We will design and synthesize subsequent generations of our lead compounds using SAR information derived from molecular modeling, activity against whole bacteria and efficacy in animals and bioavailability studies. Aim 2: In Vitro and In Vivo Antibacterial Activity against B. pseudomallei. The in vitro activity of the current diphenyl ether compounds against 8. pseudomallei will be assessed by determining (i) the IC50 for inhibition of the 8. pseudomallei Fabl enzyme (FablBpm), (ii) antibacterial activity (MIC and MBC) (iii) toxicity, PK/PD and deliverability. Selected compounds will be progressed to efficacy testing in the 8. pseudomallei animal model of infection. Aim 3: Extension to Y. pestis. We will extend our antibacterial discovery efforts to include the pathogen Y. pestis. Testing will be conducted using the established approach and compounds with appropriate activity will be evaluated in animal models of infection. This research project fits within the RMRCE Integrated Research Focus on Bacterial Therapeutics, and will interact directly with RP 2.1, RP 2.2, RP 2.5 and RP 2.6, and utilize the resources of Core C and Core E.